Inorganic arsenic removal by zero-valent iron

Zero-valent iron can be used to remove inorganic arsenic from aqueous solut ions. The mechanism for arsenic removal appears to be a surface precipitati on or adsorption of arsenic with iron. This mechanism differs significantly from the removal mechanisms of chlorinated hydrocarbons (reductive dechlor ination) and chromium(VI) reduction accompanied by hydroxide precipitation. Arsenic removal efficiencies of greater than 95% are observed in laborator y and field-column studies. Arsenate is removed more effectively than arsen ite; however, effective arsenite removal occurs even under anoxic condition s. The removal efficiency is related to the surface area or the type of iro n used and improved over time, possibly due to pitting of the iron surface and increased surface area for sorption due to iron corrosion and ferrous i ron adsorption/precipitation. Preliminary results indicate that arsenic is tightly bound to the iron filings, and only a small percentage is readily l eached. This finding coupled with the results of field experiments and spec troscopic analysis (SEM/EDX and XPS) provide evidence that surface precipit ation is the predominant removal mechanism.